A channel electric inductor assembly can be used with a vessel for holding molten metal in an industrial process. FIG. 1(a) illustrates in cross section, a typical channel electric inductor assembly 110. An outer shell 112 generally provides structural support for the assembly. The inner walls of the shell are lined with heat insulating refractory 114. Bushing 116, generally cylindrical in shape, serves as a housing for a coil and core assembly comprising inductor coil 118a and transformer core 118b. Bushing 116 provides support, as well as cooling, of refractory wall 114 surrounding the coil and core assembly. The exterior wall of the bushing is lined with heat insulating refractory 114. The space between the refractory adjacent to the inner walls of the shell and the refractory surrounding the bushing defines a metal flow channel. The channel electric assembly illustrated in FIG. 1(a) is known as a single loop type, since metal flows around the single loop formed by the coil and core assembly in bushing 116. When an ac current flows through inductor 118a, electrically conductive metal is inductively heated and moved through the flow channel of the loop, for example, in the direction of the arrows shown in FIG. 1(a). The channel electric inductor assembly 110 is typically coupled with a vessel 130 (also referred to as an upper case) for holding molten metal as illustrated in FIG. 1(b). The vessel may be formed from a structurally supporting outer wall 132 that is suitably lined with refractory 134. By circulation of metal from vessel 130 through the flow channel of the loop, the metal in vessel 130 can be heated or held at a desired process temperature for use in an industrial process. For example, the metal in the vessel may be a zinc composition, and a metal strip may be dipped into the vessel to zinc coat the strip.
In fabrication of the channel electric induction assembly, not only must the flow channel be created, but also the boundary walls of the flow channel, which comprise porous refractory, must be suitably prepared to withstand seepage of molten metal into the refractory. Typically the refractory wall material is sintered; that is, heat is applied to the refractory walls of the flow channel at a temperature below the melting point of the refractory composition, but at a high enough temperature to bond the particles of the refractory together at the boundary wall to form a substantially impervious boundary to molten metal moving through the flow channel. A traditional way of accomplishing the formation of the flow channel and sintering of the refractory wall material is to use a combustible channel mold, such as a mold formed from wood, for the flow channel. The mold is shaped to conform to the volume of the flow channel of the loop. After refractory is installed around the combustible channel mold, the mold is ignited and burned to remove the mold by combustion, and also to sinter the refractory walls of the flow channel by the heat of combustion. This is referred to as using a combustible mold. A disadvantage of this method is that the rate of combustion throughout the entire volume of the channel mold is not generally controllable. Therefore the degree of sintering of the refractory wall along the entire flow channel is not of consistent quality, and local areas of improperly sintered refractory wall results. Seepage of molten metal from the flow channel into refractory 114 can result in metal leakage to the outer shell and/or to the inductor coil and core assembly, which can cause premature failure of the channel electric inductor assembly.
A nonremovable channel mold can be formed, for example, from an electrically conductive metal. After assembly of the channel electric inductor assembly with the electrically conductive metal mold positioned in what will become the flow channel, an ac current is applied to inductor coil 118a to inductively melt the electrically conductive channel mold. A disadvantage of this method is that electric induction heating and melting of the electrically conductive metal mold makes it difficult to reach sintering temperature of the refractory before the mold melts. Further the mold may be formed from welded sections, and rapid induction melting of the welds will cause sections of the mold to inductively melt in an irregular manner. Therefore, there is the need for a channel electric inductor assembly with a nonremovable channel mold that can be used to properly sinter the refractory walls of the flow channel and then be satisfactorily consumed.